In a publication entitled "Stationary Mirror Systems for Solar Collectors" by H. Tabor which appears in Solar Energy, Vol. II, Nos. 3-4, July-October 1958, at pages 27-33, there is defined an angle in solar geometry called the EWV altitude. In the course of a day, the sun moves over a large angle as it sweeps the sky from sunrise to sunset. It also has a smaller angular movement related to the rise and fall of the sun. In the publication by Tabor this smaller angular variation due to the altitude variation of the sun, which is both a daily and annular phenomenon is termed EWV altitude. Correction of solar collector position to account for the variation of EWV altitude is usually limited to variation in the seasonal tilt of the collector in accordance with the changes in the declination angle of the sun for a particular location. Correction for daily changes in the sun's altitude which would permit a reduced angle of acceptance for a cylindrical, solar radiant energy collector has not been practicable due to the involved equipment necessary.
In cylindrical, radiant energy collectors, such as described in a publication by R. Winston appearing in Solar Energy, Vol. 16, No. 2, at pages 89-95, (1974) and in a prior U.S. application Ser. No. 492,074, entitled "Radiant Energy Collector," filed on July 25, 1974, now U.S. Pat. No. 4,002,499 and in the above-referred Tabor article, the collector configuration is determined by the angle of acceptance. The concentration factor is roughly inversely proportional to this angle so that the greater the angle, the less the concentration factor but the longer is the period of collection. If a collector could be provided which would allow reduced angle of acceptance without decrease in the hours of collection, higher concentration and simplified design of the collector would be achieved. In particular, in nonimaging cylindrical collection devices, the high concentration factors which are attainable are off-set by the large reflective surface area required for high concentration. By providing a means for varying the daily tilt of the collector according to the variation in the sun's EWV altitude, a truncated, cylindrical collector, i.e. one with shortened side walls and therefore less reflector area, can achieve as good a concentration as the untruncated collector. Thus the reflector utilization factor is improved. Improvement in the reflector utilization factor is also obtained in other concentrators, with increased concentration.
It is therefore an object in this invention to provide an improved solar collector.
Another object of this invention is to provide a means for varying the tilt of a solar, radiant energy collector in response to the daily variation in the sun's EWV altitude.